The present invention relates to a new and improved tool for machining tooth flanks, in particular the tooth flanks of a hardened workpiece having pre-formed teeth, and also pertains to a method of finishing or microfinishing tooth flanks.
In its more particular aspects the tool of the present development is of the type comprising at least one cutting blade or plate holder and at least one cutting blade or plate mounted or fastened thereto. The cutting blade comprises a base member or backing, particularly made of a hard metal, typically tungsten carbide, and a sintered-on cover layer formed of a very hard polycrystalline cutting material, in particular cubic boron nitride. The cutting blade forms a cutting surface and a clearance surface.
A cutting blade is known from the Journal "Werkstatt and Betrieb", Volume 114, Issue No. 1, pages 45 to 49, 1981 which comprises a hard metal base member having a thickness of 4.76 mm and a cover layer made of cubic boron nitride having a thickness of 0.89 mm which is sintered onto the base member at high pressure and high temperature. Such cutting blades have been successfully employed for machining or turning hardened steels. To that end the cutting blades have been chucked in a clamping holder such that the surface of the cover layer made of cubic boron nitride formed the cutting or rake surface and there resulted a tool geometry having a negative rake angle of -6.degree..
The applicants have found that such cutting blades are also suited for chip machining tooth flanks, particularly hardened tooth flanks. The unavoidable intermittent action of the tool upon the workpiece, however, increases the danger that the sintered-on cover layer will crumble away at the cutting edges. For this reason and because of the generally high surface finish requirements which are placed upon the tooth flanks, in particular upon hardened tooth flanks which are not subsequently ground, it is necessary to specifically observe that the cutting blades are maintained in a sharp condition by timely re-grinding the same. In so doing, however, care must be taken to ensure that the profile of the tool, which for the machining of tooth flanks, such as gear tooth flanks, generally corresponds to a rack or to an individual tooth or to an individual tooth flank of a rack, is preserved as precisely as possible. It is therefore general practice to re-grind the tools used for chip machining tooth flanks only at their cutting or rake surfaces. When, however, the cutting blades or plates are arranged in conventional manner such that the sintered-on cover layer forms the cutting surface, then special experience and apparatus are required for regrinding this cutting surface, which are only available in specialized plants or enterprises.